Dactylosternum latum (Sharp, 1873) Fikacek et al., 2015

Mai, Zuqi, Hu, Jian, Minoshima, Yûsuke N., Jia, Fenglong & Fikáček, Martin, 2022, Review of Dactylosternum Wollaston, 1854 from China and Japan (Coleoptera, Hydrophilidae, Sphaeridiinae), Zootaxa 5091 (2), pp. 269-300 : 297-298

Occurrence of D. latum in Japan

Dactylosternum latum was described based on the Japanese specimens, but the occurence of the species in Japan is questionable. Three possibilities arise from this and previous studies: (1) the type specimens were mislabelled; (2) the species is extremely rare or occurs in uncommon habitats, and thus it has been overlooked; or (3) this species has already become extinct in Japan.

Mislabelled specimens are not rare in any collection, and mislabelling would imply that the actual collection locality is outside Japan. Similar cases have been recognized in some Japanese beetles collected in Nagasaki by G. Lewis; for example, Tenebrio alternicostis Marseul, 1876 (Tenebrionidae) and Eotrichia niponensis ( Lewis, 1895) ( Marseul 1876; Lewis 1895) have never been collected in Japan since the original description at present ( Kobayashi 1982; Akita & Masumoto 2016); the latter species was also recorded from Russian Far East and China ( Bezděk 2016). On the request of the loan of the type specimens, we also received one additional unidentified female specimen of Chinese Dactylosternum from D. Sharp collection in NHM. The specimen is identical to D. latum in dorsal and ventral external characters and there is a high probability that it belongs to the species. Moreover, we found additional specimens of D. latum from China. These findings raise the possibility that D. latum may be native to south China and Laos and the real origin of the type specimens of C. latum is China.

Alternatively, habitat loss associated with environmental destruction has long been serious in Japan as well as in other biodiversity hotspots. It is not impossible that the species has already become extinct or is exceedingly rare at present. Dactylosternum latum has been neglected and it has never been figured in any literature. Hence, it is still possible that it has been overlooked and is preserved in cabinets as unidentified Coleoptera .

Beetle fauna has been rather well studied in Japan; it is therefore difficult to assume that no entomologist has ever encountered D. latum over the past 150 years. Moreover, Dactylosternum is a terrestrial lineage ( Hansen 1991), and its occurrence in aquatic habitats is questionable. We therefore consider the possibility that the locality as well as the habitat data are doubtful. However, at present, we cannot rule out any possibilities based on our poor knowledge of the species. We expect that this study may help to discover more recently collected specimens and help us to understand the distribution of the species.